During the fabrication of semiconductor devices, it is often advantageous to accurately measure the temperature of the device being processed. One method of temperature measurement is to use a thermocouple in contact with the surface which needs to be measured. Another contact measurement technique utilizes a phosphorescent sensor.
However, the standard contact measurement technique is not suitable due to possible metal contamination of the semiconductor material at the point of contact and subsequent diffusion of such contaminants throughout the wafer. In addition, attachment of a thermocouple leads to "shadowing" of the wafer to the incoming radiation, and also a perturbation of its own radiation and internal heat transfer.
Non-contact measurement techniques such as pyrometry may also be used. This technique, however, is of limited usefulness for semiconductors. A serious drawback is that at temperatures below approximately 700.degree. to 800.degree. C., significant amounts of radiation pass from the heating lamps through the wafer to the pyrometric detector and thus interfere with the measurement of the wafer temperature. In addition, the emissivity of a silicon surface, upon which temperature determination by pyrometry is based, varies with temperature, doping level and film deposition. These variations lead to inaccurate temperature assignment.
Accordingly, improvements which overcome any or all of the problems are presently desirable.